Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$141.91	11.447%	$158.1544	$158.15	$158.15	$158.20
Purchase #2	$242.84	4.322%	$253.3355	$253.34	$253.35	$253.30
Purchase #3	$200.76	10.535%	$221.9101	$221.91	$221.90	$221.90
Purchase #4	$40.78	13.404%	$46.2462	$46.25	$46.25	$46.20
Purchase #5	$242.50	10.848%	$268.8064	$268.81	$268.80	$268.80
Purchase #6	$179.65	4.304%	$187.3821	$187.38	$187.40	$187.40
Purchase #7	$30.51	3.367%	$31.5373	$31.54	$31.55	$31.50
7 purchase totals =	$1,078.95		$1,167.3720	$1,167.38	$1,167.40	$1,167.30